Methods and devices for analyzing a sensor element are available, the sensor element outputting a signal as a function of a measured variable.
It has been suggested that for controlling internal combustion engines, the combustion chamber pressure is determined, in addition to other measured variables. Multiple publications describe technical approaches for detecting the combustion chamber pressure.
Measuring sensors or sensor elements which operate according to the piezoelectric principle appear particularly attractive. A suitable material, such as quartz or a sintered ceramic material, is subjected to the combustion chamber pressure. The material is, for example, installed as a disk in a suitable housing and mounted in a conventional way in a cylinder head as a combustion chamber pressure sensor. Furthermore, integration into an already existing component, such as a spark plug or glow plug, is conventional. A charge, which is proportional to the pressure, arises in the material of the sensor element subjected to the combustion chamber pressure, which may be converted into a voltage signal using a suitable electronic circuit, e.g., a charge amplifier or impedance transformer. This voltage is processed further in an engine control unit and incorporated into different closed-loop and open-loop controls of the engine. The combustion chamber pressure of each cylinder of the internal combustion engine is typically sampled synchronously with a crankshaft angle, for example, at a resolution of 1° crankshaft angle.
If a piezoceramic material, such as the sintered ceramic material, is used for the measuring sensor or the sensor element, it is distinguished by a comparatively high sensitivity, i.e., it generates a greater charge at a given pressure than quartz. A disadvantage in this case is the pronounced temperature dependence of the sensitivity in such piezoceramic materials. Therefore, determining the temperature of the sensor element would be advantageous, in order to be able to suitably compensate for the temperature error in subsequent signal processing.
Conventional approaches include mounting a temperature sensor in the proximity of the sensor element to detect the combustion chamber pressure, also referred to in the following as a combustion chamber pressure sensor. Alternatively, the temperature error may also be compensated for using a capacitive charge divider, the corresponding capacitor of the capacitive charge divider having to have the same temperature as the combustion chamber pressure sensor. This is described in “A. Peterson, Temperaturkompensation piezokeramischer Sensoren [Temperature Compensation of Piezoceramic Sensors], Elektronikindustrie 12-1988.” Both of these methods have the disadvantage of requiring that still further components be housed in the already restricted installation space of the combustion chamber pressure sensor.